The present invention is directed to a bonding amalgam and method of making for bonding two articles together, and in particular for providing a novel class of metals for bonding in electronic packaging and interconnect applications.
Bonding is probably the most neglected stage in the manufacturing sequence of electronic and microelectronic devices and assemblies. Most recent activity in the development of bonding materials has been directed toward polymer-based adhesives, which do not meet military standards. If metal alloys are required, then only traditional solders are available. Solders are unsatisfactory as they are subject to thermal cycle fatigue, require high bonding temperatures producing stress in the article being soldered, and have upper temperature limitations at their melting points.
It has been suggested in U.S. Pat. No. 3,141,238 that amalgams can be used for bonding in a manner analogous to their use in dentistry. An amalgam is a mechanically alloyed composition formed by a liquid metal and a metal powder. Amalgams in general have low processing temperatures, down to near room temperature, yet they yield materials with thermal stabilities between 250 and 600 degrees C. depending upon the materials. However, the composition and formulation of the compositions Of materials called amalgams in the prior art have not provided satisfactory bonding in electronic applications. Dental applications of amalgams rely upon a mechanical locking of the filler in the dental cavity because of a slight expansion of the amalgam. But in electronics, bonds involving adhesion and metallurgical interaction between surfaces are required and neither the dental amalgams nor the prior art materials can satisfactorily achieve this.
The present invention is also directed to a method of making a bonding amalgam that will achieve bonding of flat and co-axial geometries for application in electronic package bonding for die attach, hermetic sealing, heat sink attachment, innerlead bonding for tape automated bonding (TAB), and via filling of through holes in ceramic substrates.